| 1 | // Copyright 2017 The Go Authors. All rights reserved. |
|---|---|
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | package shift |
| 6 | |
| 7 | // Simplified dead code detector. |
| 8 | // Used for skipping shift checks on unreachable arch-specific code. |
| 9 | |
| 10 | import ( |
| 11 | "go/ast" |
| 12 | "go/constant" |
| 13 | "go/types" |
| 14 | ) |
| 15 | |
| 16 | // updateDead puts unreachable "if" and "case" nodes into dead. |
| 17 | func updateDead(info *types.Info, dead map[ast.Node]bool, node ast.Node) { |
| 18 | if dead[node] { |
| 19 | // The node is already marked as dead. |
| 20 | return |
| 21 | } |
| 22 | |
| 23 | // setDead marks the node and all the children as dead. |
| 24 | setDead := func(n ast.Node) { |
| 25 | ast.Inspect(n, func(node ast.Node) bool { |
| 26 | if node != nil { |
| 27 | dead[node] = true |
| 28 | } |
| 29 | return true |
| 30 | }) |
| 31 | } |
| 32 | |
| 33 | switch stmt := node.(type) { |
| 34 | case *ast.IfStmt: |
| 35 | // "if" branch is dead if its condition evaluates |
| 36 | // to constant false. |
| 37 | v := info.Types[stmt.Cond].Value |
| 38 | if v == nil { |
| 39 | return |
| 40 | } |
| 41 | if !constant.BoolVal(v) { |
| 42 | setDead(stmt.Body) |
| 43 | return |
| 44 | } |
| 45 | if stmt.Else != nil { |
| 46 | setDead(stmt.Else) |
| 47 | } |
| 48 | case *ast.SwitchStmt: |
| 49 | // Case clause with empty switch tag is dead if it evaluates |
| 50 | // to constant false. |
| 51 | if stmt.Tag == nil { |
| 52 | BodyLoopBool: |
| 53 | for _, stmt := range stmt.Body.List { |
| 54 | cc := stmt.(*ast.CaseClause) |
| 55 | if cc.List == nil { |
| 56 | // Skip default case. |
| 57 | continue |
| 58 | } |
| 59 | for _, expr := range cc.List { |
| 60 | v := info.Types[expr].Value |
| 61 | if v == nil || v.Kind() != constant.Bool || constant.BoolVal(v) { |
| 62 | continue BodyLoopBool |
| 63 | } |
| 64 | } |
| 65 | setDead(cc) |
| 66 | } |
| 67 | return |
| 68 | } |
| 69 | |
| 70 | // Case clause is dead if its constant value doesn't match |
| 71 | // the constant value from the switch tag. |
| 72 | // TODO: This handles integer comparisons only. |
| 73 | v := info.Types[stmt.Tag].Value |
| 74 | if v == nil || v.Kind() != constant.Int { |
| 75 | return |
| 76 | } |
| 77 | tagN, ok := constant.Uint64Val(v) |
| 78 | if !ok { |
| 79 | return |
| 80 | } |
| 81 | BodyLoopInt: |
| 82 | for _, x := range stmt.Body.List { |
| 83 | cc := x.(*ast.CaseClause) |
| 84 | if cc.List == nil { |
| 85 | // Skip default case. |
| 86 | continue |
| 87 | } |
| 88 | for _, expr := range cc.List { |
| 89 | v := info.Types[expr].Value |
| 90 | if v == nil { |
| 91 | continue BodyLoopInt |
| 92 | } |
| 93 | n, ok := constant.Uint64Val(v) |
| 94 | if !ok || tagN == n { |
| 95 | continue BodyLoopInt |
| 96 | } |
| 97 | } |
| 98 | setDead(cc) |
| 99 | } |
| 100 | } |
| 101 | } |
| 102 |
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